Purification device for decreasing particulate matter and nitrogen oxides in diesel engine

ABSTRACT

A diesel exhaust purification device for decreasing the amount of particulate matter and nitrogen oxides includes a Catalyzed Diesel Particulate Filter (CDPF) disposed in an exhaust conduit to capture particulate matter (PM). A differential pressure sensor detects the amount of PM contained in the CDPF. A post-injection injector is in the exhaust conduit. A Diesel Fuel Decomposition Catalyst (DFC) forms a reducing agent by decomposing the fuel injected from the post-injection injector. A nitrogen oxide adsorbing catalyst reduces nitrogen oxides accumulated therein and removes them using the reducing agent. A nitrogen oxide sensor in the exhaust conduit detects the amount of nitrogen oxides in exhaust gases. A control unit determines the regeneration time of the CDPF from signals detected by the differential pressure sensor, controls the amount of the fuel post-injected, determines the regeneration time of the nitrogen oxide adsorbing catalyst from signals detected by the nitrogen oxide sensor, controls the fuel post-injected through the post-injection injector.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on, and claims priority from, Korean Application Serial Number 10-2006-0115167, filed on Nov. 21, 2006, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to a purification device for diesel engine exhaust and, more particularly, for decreasing particulate matter and nitrogen oxides contained in exhaust gases of diesel engines.

BACKGROUND OF THE INVENTION

Generally, in a conventional purification device for decreasing both particulate matter and nitrogen oxides contained in exhaust gases of diesel engines, a Catalyzed Diesel Particulate Filter (CDPF), a nitrogen oxide adsorbing catalyst (de-NOx catalyst) and a Diesel Oxidation Catalyst (DOC) are disposed in sequence in an exhaust conduit, a subsidiary exhaust conduit branched from the exhaust conduit is disposed in the exhaust conduit at a position located in front of the Catalyzed Diesel Particulate Filter (CDPF), an on-off valve, a secondary injection system and a Diesel Fuel Decomposition Catalyst (DFC) are disposed in the subsidiary exhaust conduit, and an outlet of the subsidiary exhaust conduit is located in front of the de-NOx catalyst.

In this case, a differential pressure sensor for detecting the amount of particulate matter (PM) accumulated in the Catalyzed Diesel Particulate Filter (CDPF) is connected to the front and rear ends of the Catalyzed Diesel Particulate Filter (CDPF), and a nitrogen oxide sensor for detecting the concentration of nitrogen oxides from exhaust gases is disposed at the rear end of the Diesel Oxidation Catalyst (DOC).

In the above conventional purification device, a reducing agent was formed by decomposing fuel using the Diesel Fuel Decomposition Catalyst (DFC), and then the formed reducing agent was supplied to the nitrogen oxide adsorbing catalyst (de-NOx catalyst). However, there has been a problem in that the Diesel Fuel Decomposition Catalyst (DFC) is rapidly oxidized depending on the condition of exhaust gases, with the result that a phenomenon of purifying exhaust gases by oxidizing fuel, rather than by decomposing fuel injected from the secondary injection system, thus forming a reducing agent, occurs.

In addition, at the time of the desulfurization activity of the nitrogen oxide adsorbing catalyst (de-NOx catalyst), which is performed behind the Catalyzed Diesel Particulate Filter (CDPF) using regeneration heat occurring at the time of the coercive regeneration of the CDPF, the fuel injected from the secondary injection system causes the Diesel Fuel Decomposition Catalyst (DFC) to catalyze rapid oxidation reactions, so that the temperature of exhaust gases at the inlet of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) is rapidly increased, with the result that the nitrogen oxide adsorbing catalyst (de-NOx catalyst) deteriorates too rapidly.

Moreover, there has been a problem in that the conventional purification device has a complicated structure, in which an additional bypass conduit, which is branched from the exhaust conduit in front of the Catalyzed Diesel Particulate Filter (CDPF) and includes an outlet in front of the nitrogen oxide adsorbing catalyst (de-NOx catalyst), is provided, and the Diesel Fuel Decomposition Catalyst (DFC) is contained in the bypass conduit.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a purification device which can reliably realize the purification for nitrogen oxides (NOx) by forming a reducing agent from fuel post-injected at the time of the regeneration of a nitrogen oxide adsorbing catalyst and regenerating the nitrogen oxide adsorbing catalyst using the reducing agent.

A purification device for decreasing particulate matter and nitrogen oxides according to an exemplary embodiment of the present invention includes a Catalyzed Diesel Particulate Filter (CDPF) disposed in an exhaust conduit to capture particulate matter (PM). A differential pressure sensor detects the amount of particulate matter (PM) contained in the Catalyzed Diesel Particulate Filter (CDPF). A post-injection injector is disposed in the exhaust conduit to post-inject fuel. A Diesel Fuel Decomposition Catalyst (DFC) forms a reducing agent by decomposing the fuel injected from the post-injection injector. A nitrogen oxide adsorbing catalyst (de-NOx catalyst) reduces nitrogen oxides accumulated therein and thus removes them using the reducing agent formed by the Diesel Fuel Decomposition Catalyst (DFC). A nitrogen oxide sensor is disposed in the exhaust conduit to detect the amount of the nitrogen oxides (NOx) contained in exhaust gases. A control unit controls the amount of fuel post-injected through the injector of a diesel engine by determining the regeneration time of the Catalyzed Diesel Particulate Filter (CDPF) from signals detected by the differential pressure sensor, and controls the amount of fuel post-injected through the post-injection injector by determining the regeneration time of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) from signals detected by the nitrogen oxide sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of the present invention, reference should be made to the following detailed description with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a purification device for decreasing particulate matter and nitrogen oxides according to a first embodiment of the present invention; and

FIG. 2 is a schematic diagram of a purification device for decreasing particulate matter and nitrogen oxides according to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings.

Referring to FIG. 1, there is shown a first exemplary embodiment of the present invention. As shown in the drawing, a Catalyzed Diesel Particulate Filter (CDPF) 14, a Diesel Fuel Decomposition Catalyst (DFC) 16 and a nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 are disposed in an exhaust conduit 12 of a diesel engine 10, respectively. A differential pressure sensor 20, which is connected to the front and rear ends of the Catalyzed Diesel Particulate Filter (CDPF) 14 and detects a pressure difference therebetween, is disposed to detect the amount of the particulate matter (PM) contained in the Catalyzed Diesel Particulate Filter (CDPF) 14. A post-injection injector 22 for post-injecting fuel and a nitrogen oxide sensor 24 for detecting the amount of nitrogen oxide (NOx) accumulated in the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 are disposed at the upstream end of the Diesel Fuel Decomposition Catalyst (DFC) 16 on the basis of an exhaust path, that is, the flow direction of exhaust gases in the exhaust conduit 12.

Here, the Catalyzed Diesel Particulate Filter (CDPF) 14 captures particulate matter (PM) contained in exhaust gases discharged through the exhaust conduit 12, and the captured particulate matter (PM) is burned and removed through fuel post-injection performed by injectors 10 a of the diesel engine 10 at the time of the regeneration of the Catalyzed Diesel Particulate Filter (CDPF) 14.

Further, the Catalyzed Diesel Particulate Filter (CDPF) 14, which is configured into a so-called “Closed Catalyst Converter” (CCC) type catalytic device, is locally coated with a Diesel Oxidation Catalyst (DOC) 14 a at the front end thereof. The Catalyzed Diesel Particulate Filter (CDPF) 14 is disposed adjacent to an exhaust manifold 11 of the diesel engine 10 so as to directly receive exhaust heat from the manifold 11.

Further, the Diesel Fuel Decomposition Catalyst (DFC) 16 forms a reducing agent by decomposing the fuel injected from the post-injection injector 22, and the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 reduces and thus removes nitrogen oxides accumulated therein using the reducing agent formed by the Diesel Fuel Decomposition Catalyst (DFC) 16.

In this case, the Diesel Fuel Decomposition Catalyst (DFC) 16 functions to convert diesel oil, which is the fuel of the diesel engine 10, into reducing agents such as carbon monoxide (CO), having high reactivity, short-chained hydrocarbons (HC) and hydrogen (H₂) by cutting and decomposing carbon chains through a catalytic reaction.

That is, the Diesel Fuel Decomposition Catalyst (DFC) 16 cuts chains of carbon constituting hydrocarbon compounds, which are main components of fuel, and thus decomposes the hydrocarbon compounds, through a thermal cracking function, as described below.

A process of decomposing fuel (Thermal Cracking):

C₁₆H₃₄→2n-C₈H₁₇*→n-C₆H₁₃*→2n-C₄H₉*→C₄H₅*→C₂H₄

C₁₆H₃₄→8 C₂H₄+H₂

(wherein, * designates radical).

Further, the Diesel Fuel Decomposition Catalyst (DFC) 16 conducts a Steam Reforming function and a Partial Oxidation function, which allow for formation of a reducing agent from the decomposed fuel, as described below.

A process of forming carbon monoxide (CO) and hydrogen (H₂), which are reducing agents, from the decomposed fuel (Steam Reforming):

C₁₆H₃₄+16 H₂O→16 CO+33 H₂

A process of forming carbon monoxide (CO), hydrocarbons (HC) and hydrogen (H₂), which are reducing agents, from the decomposed fuel (Partial Oxidation):

C₁₆H₃₄+½ O₂→8 C₂H₄+H₂O

C₁₆H₃₄+8 O₂→16 CO+17 H₂.

Accordingly, the reducing agent formed by the Diesel Fuel Decomposition Catalyst (DFC) 16 prevents a rapid oxidation reaction generated in the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 by directly reacting the fuel injected from the post-injection injector 22 with the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18, thereby preventing the deterioration of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 due to an oxidation reaction.

As a result, the Diesel Fuel Decomposition Catalyst (DFC) 16 can reduce adsorbed nitrogen oxide (NOx) to nitrogen (N₂).

Meanwhile, the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 constitutes a catalytic device which is locally provided with a reducing agent forming catalyst 18 a at the upstream end thereof on the basis of the exhaust path, like the Diesel Fuel Decomposition Catalyst (DFC) 16 described previously, thus forming the reducing agent by decomposing the fuel injected from the post-injection injector 22.

More specifically, the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 essentially includes a catalyst coated portion for purifying nitrogen oxides, and additionally includes a further coated portion of the reducing agent forming catalyst 18 a at the front end thereof, which supplements the function of the Diesel Fuel Decomposition Catalyst (DFC) 16, that is, which forms the reducing agent by decomposing fuel. Consequently, since the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 partially includes the reducing agent forming catalyst 18 a, the Diesel Fuel Decomposition Catalyst (DFC) 16, which is relatively expensive, can be used in a decreased amount.

A control unit 26 determines the regeneration time of the Catalyzed Diesel Particulate Filter (CDPF) 14 from signals detected by the differential pressure sensor 20, and determines the regeneration time of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 from signals detected by the nitrogen oxide sensor 24. A control unit 26 may comprise a processor, accessory and associated hardware and software as may be selected and programmed by a person of ordinary skill as it is based on the teachings of the present invention as set forth herein.

In this case, the control unit 26 controls the amount of the fuel post-injected through injectors 10 a by controlling the operation of the injectors 10 a of a diesel engine 10 when determining the regeneration time of the Catalyzed Diesel Particulate Filter (CDPF) 14 through the differential pressure sensor 20, and the control unit 26 controls the amount of the fuel post-injected through the post-injection injector 22 by controlling the operation of the post-injection injector 22 when determining the regeneration time of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 through the nitrogen oxide sensor 24.

Moreover, in the present invention, the Diesel Fuel Decomposition Catalyst (DFC) 16 is located at the upstream end of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 on the basis of an exhaust path, and the Catalyzed Diesel Particulate Filter (CDPF) 14 is located at the upstream end of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 on the basis of an exhaust path. According to the first embodiment of the present invention, the Catalyzed Diesel Particulate Filter (CDPF) 14 is configured to be located in front of the Diesel Fuel Decomposition Catalyst (DFC) 16. In this case, the Diesel Fuel Decomposition Catalyst (DFC) 16 and the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 are sequentially disposed in the same housing.

Referring to FIG. 2, there is shown a second exemplary embodiment of the present invention. According to this second embodiment, a Diesel Fuel Decomposition Catalyst (DFC) 16 is configured to be located upstream of a Catalyzed Diesel Particulate Filter (CDPF) 14 on the basis of an exhaust path. In this case, the Diesel Fuel Decomposition Catalyst (DFC) 16 and a nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 are spaced apart from each other and sequentially disposed in separate housings.

According to the first and second embodiments of the present invention, the post-injection injector 22 is located on an exhaust conduit 12 in front of the Diesel Fuel Decomposition Catalyst (DFC) 16, and the nitrogen oxide sensor 24 is located on the exhaust conduit 12 in front of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18. In this case, the nitrogen oxide sensor 24 detects the amount of nitrogen oxides (NOx) contained in exhaust gases flowing through the exhaust conduit 12 in real time and then outputs them to the control unit 26. The control unit 26 estimates the amount of nitrogen oxides (NOx) accumulated on the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 through signals input from the nitrogen oxide sensor 24, compares the amount of the accumulated nitrogen oxides (NOx) with the capacity of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18, and then calculates the regeneration time of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18. As a result, the control unit 26 can more accurately calculate the regeneration time of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18, therefore the emission of the nitrogen oxides (NOx) can be more positively prevented.

Hereinafter, an operation of the purification device for decreasing particulate matter and nitrogen oxides according to the present invention will be described.

First, when exhaust gases are discharged through an exhaust conduit 12 after the burning in the diesel engine 10, particulate matter (PM) contained in the exhaust gases is captured in the Catalyzed Diesel Particulate Filter (CDPF) 14, and nitrogen oxides (NOx) are accumulated in the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18.

In the course of these processes, the control unit 26 determines the regeneration time of the Catalyzed Diesel Particulate Filter (CDPF) 14 through the differential pressure sensor 20. When the regeneration time thereof is reached, the control unit 26 outputs post-injection signals to the injectors 10 a of the diesel engine 10 and then removes the particulate matter (PM) captured through the post-injected fuel by oxidizing it.

Further, the control unit 26 determines the regeneration time of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 through the nitrogen oxide sensor 24. When the regeneration time thereof is reached, the control unit 26 outputs post-injection signals to the post-injection injector 22. The fuel post-injected through the post-injection injector is converted into reducing agents such as carbon monoxide (CO) having a high reactivity, short-chained hydrocarbons (HC) and hydrogen (H₂) through the Diesel Fuel Decomposition Catalyst (DFC) 16 and the reducing agent forming catalyst 18 a, and is then supplied to the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18.

In this case, the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 reduces the accumulated nitrogen oxides (NOx) to nitrogen (N₂) through the supplied reducing agents and then discharges them. As a result, a rapid oxidation reaction, generated by directly reacting the fuel post-injected from the post-injection injector 22 with the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 can be prevented, thereby preventing damage to the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 due to the deterioration thereof.

Further, according to the present invention, a process of desulfurizing and regenerating exhaust gases at high temperature, which is usually performed to remove a poisonous sulfur coating, which is the result of sulfur components contained in diesel fuel, from the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18, is not additionally performed, and the desulfurization and regeneration of the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 using exhaust heat transferred from an exhaust manifold 11 of the diesel engine 10 can be realized using heat discharged at the time of the regeneration of the Catalyzed Diesel Particulate Filter (CDPF) 14.

That is, a heat source necessary for a process of desulfurizing the nitrogen oxide adsorbing catalyst (de-NOx catalyst) 18 can be obtained from exhaust heat generated in the process of regenerating the Catalyzed Diesel Particulate Filter (CDPF) 14, which is generated by the post-injection of fuel through the injectors 10 a of the diesel engine 10, thereby improving an air-fuel ratio by decreasing the amount of fuel that is post-injected.

As described above, the purification device for decreasing particulate matter and nitrogen oxides according to the present invention forms a reducing agent by decomposing the fuel that is post-injected at the time of the regeneration of the nitrogen oxide adsorbing catalyst through the diesel fuel decomposition catalyst, prevents damage to the nitrogen oxide adsorbing catalyst due to the deterioration thereof, resulting from overheating of the nitrogen oxides and the catalyst by the oxidation reaction at the time of the regeneration of the nitrogen oxides accumulated in the nitrogen oxide adsorbing catalyst using the formed reducing agent, thereby realizing the normal removal of the nitrogen oxides. 

1. A purification device for decreasing particulate matter and nitrogen oxides, comprising: a filter disposed in an exhaust conduit to capture particulate matter; a differential pressure sensor for detecting an amount of the particulate matter contained in said filter; a post-injection injector disposed in the exhaust conduit to post-inject fuel; a first catalyst for forming a reducing agent by decomposing the fuel injected from the post-injection injector; a second catalyst for reducing nitrogen oxides accumulated therein and thus removing them using the reducing agent formed by the catalyst; a nitrogen oxide sensor disposed in the exhaust conduit to detect an amount of nitrogen oxides contained in exhaust gases; and a control unit for determining a regeneration time of said filter from signals detected by the differential pressure sensor and controlling an amount of the fuel post-injected through injectors of a diesel engine, and determining a regeneration time of the second catalyst from signals detected by the nitrogen oxide sensor and controlling the amount of the fuel post-injected through the post-injection injector.
 2. The purification device as defined in claim 1, wherein: said filter is a catalyzed diesel particulate filter;
 3. The purification device as defined in claim 2, wherein the catalyzed diesel particulate filter is directly connected to an exhaust manifold and is a closed catalyst converter type catalytic device partially provided with a diesel oxidation catalyst.
 4. The purification device as defined in claim 2, wherein the nitrogen oxide adsorbing catalyst is a catalytic device partially provided with a reducing agent forming catalyst, which forms the reducing agent by decomposing fuel.
 5. The purification device as defined in claim 2, wherein the diesel fuel decomposition catalyst is located upstream of the nitrogen oxide adsorbing catalyst on a basis of an exhaust path, and the catalyzed diesel particulate filter is located upstream of the nitrogen oxide adsorbing catalyst on a basis of an exhaust path.
 6. The purification device as defined in claim 5, wherein the catalyzed diesel particulate filter is located upstream of the diesel fuel decomposition catalyst on a basis of an exhaust path.
 7. The purification device as defined in claim 5, wherein the diesel fuel decomposition catalyst is located upstream of the catalyzed diesel particulate filter on a basis of an exhaust path.
 8. The purification device as defined in any one of claims 2 to 7, wherein the post-injection injector is located in front of the diesel fuel decomposition catalyst in an exhaust conduit.
 9. The purification device as defined in claims 8, wherein the nitrogen oxide sensor is located in front of the nitrogen oxide adsorbing catalyst in an exhaust conduit. 